Lysine Requirement of Growing Pigs at Two Levels of Dietary Protein

Abstract

Two-hundred-forty crossbred pigs weighing 18 kg initially were assigned to dietary lysine levels ranging from .43% to .91% (.08% increments) at either 16% or 12% dietary crude protein. The dietary protein came from corn, sesame meal and crystalline amino acids. Diets were formulated to contain levels of all amino acids except lysine consistent with the most recent N.R.C. requirement pattern at 16% protein. Lysine addition to the basal diets resulted in a quadratic response in gain, feed intake and gain/feed ratio. Protein level did not significantly affect rate of gain, but feed intake was significantly greater by pigs fed diets with 12% protein than by those fed 16% protein. The interaction between protein level and lysine level was statistically significant for rate of gain. Thus, in the linear area of growth (i.e., the lower levels of lysine) pigs fed the 12% protein diets gained faster than those fed the 16% protein diets. At higher levels of lysine, however, pigs fed 16% protein gained more rapidly than those fed 12% protein. Also, at the lower levels of lysine, gain/feed ratio was similar for pigs at both protein levels, but at higher lysine levels, pigs fed 16% protein gained more efficiently than those fed 12% protein. Using pooled data, dietary lysine requirements for maximal gain were estimated by least squares analysis to be .77% at 16% and .69% at 12% protein. The dietary lysine requirement of growing pigs decreased .02% of the diet for each 1% decrease in the level of dietary protein. This concept was tested using corn-soybean meal diets. A 14% protein diet containing supplemental lysine to bring the dietary level to .73% allowed performance similar to that obtained with a 16% protein diet (.77% lysine) or a 14% protein diet fortified with crystalline lysine to contain .77%.